The Most Exciting Sentence I’ve Read This Decade…

…Would be this one:

 We find an excess of B -mode power over the base lensed- CDM expectation in the range 30 < ` <  150, inconsistent with the null hypothesis at a significance of >  5 δ.

That’s from the abstract to this paper, released yesterday, in which the team using the BICEP microwave detector at the South Pole reports on their analysis of three years of data taken from 2010-2012.

So what’s that all about?  It’s the best evidence yet that a fundamental pillar of Big Bang cosmology is right, that a concept named inflation does in fact describe what happened within the first instant of the formation of our universe.  Here’s how Alan Guth, the inventor of the idea describes it:

This theory is a new twist on big bang theory, proposing a novel picture of ho the universe behaved for the first minuscule fraction of a second of its existence.

The central feature of the theory is a brief period of extraordinary rapid expansion, of inflation,  which lasted for a time interval perhaps as short as 10^-30 seconds.  During this period the universe expanded by at least a factor of 10^25, and perhaps a great deal more. [Alan Guth, The Inflationary Universe, p. 14.]

Guth’s initial version of inflation theory has been refined significantly since its origins in the late 1970s, and in its modern form inflation has become part of the basic toolkit of cosmological investigation.  The universe we observe doesn’t make sense unless something occurred to explain, for just one example, the way the universe looks basically the same everywhere, when viewed on the largest scale.  Inflation as the idea has evolved has become the best available explanation (though there have been competing models) for this and other observed cosmological properties.  But the challenge has been to find some tell-tale sign that shows* that inflation actually happened.

It’s been clear for a long time where such signs might lie:  in the cosmic microwave background (CMB),  a snapshot of the cosmos taken at a moment called “recombination,” when the universe cooled down enough to permit electrons and protons to come together to form (mostly) neutral hydrogen atoms.  Photons — light — that up till that moment had been embraced in electromagnetic dances with charged particles were then unshackled to fly freely through space, carrying with them the traces of where they’d been just before that liberation — which came just 380,000 years after the big bang.


Over time (13.8 billionyears), thatextremely hot (energetic) spray of light has cooled to 2.7 Kelvins — 2.7 degrees above absolute zero — and is now detectable as those very long wavelengths of light called microwaves.  This  microwave background was identified in 1965 as a generalized blur covering the entire sky; increasingly sophisticated measurements have revealed more and more detail.  Over the last twenty fiveyears those observations have turned into a probe of what happened between the big bang and the flash of the CMB itself:  each newly precise measurement constrains the possible physics that gave rise to the details thus revealed.  Step by step, each new level of detail narrow the options for what could have occurred during the big bang era — and the chain of events that lead from cosmic origins to us becomes increasingly clear.

In the 1990s,  improving resolution of CMB images revealed spots on the sky where there is slightly more energy in that microwave background — corresponding to regions in the early universe with slightly more matter-energy than surrounding regions.  Such variations account for why there are lots of galaxies full of stars in some places, and vast voids in other:  over millions and billions of years, gravity can work on very slight variations in initial density to sort matter into that kind of pattern.

With the advance of both space and ground based microwave imagers, it’s become possible to sample the CMB in vastly greater detail, and thus uncover much more than the simple (easy for me to say) evolution of structure in the universe.  For example, CMB researchers have identified several acoustic peaks in the background — literally, the ringing of the early universe, pressure waves produced by the interaction of light and matter in the very early universe.  The particular properties of those peaks reveal basic facts about the universe — and help distinguish between different theories about how we get the cosmos we inhabit from the big bang whose traces we see in the CMB.

Before today, the state of play was that CMB results were most consistent with the  predictions of inflation, compared with other candidate ideas.  At the same time though, observations that are consistent-with are not the same as direct observations of the cosmological equivalent of the miscreant’s fingerprints on the knife.  That’s what the BICEP results deliver.

In simplest terms:  modern theories of cosmic inflation say that immediately after some tiny perturbation occurs that marks the birth of a universe, it gets pulled apart by inflation — which you can think of as negative gravity, a gravitational field that stretches space-time.  The inflationary episode is so powerful that it expands the infant universe by orders of magnitude in fractions of a second — as some say, inflation provides the bang in the big bang — and it’s so violent that as space-time undergoes such wild tugs, ripples form.  Those ripples are gravitational waves — predicted by Albert Einstein, inferred from the behavior of pulsars, but never detected directly.  An observation of such primordial fluctuations, variations in the strength of the gravitational field from point to point in the early universe, would offer the first direct glimpse of traces of an inflationary episode marking the birth of our cosmos.

And that’s what BICEPs results contain:  the team led by John Kovac at the Harvard – Smithsonian Center for Astrophysics, Clem Pryke at the University of Minnesota, Jamie Bock at Caltech/JPL, and Chao-Lin Kuo of Stanford and SLAC report the detection of the signature of gravity waves in the CMB with the properties corresponding to those predicted to be produced by inflation.

In slightly more detail, the BICEP experiment observed a particular pattern of polarization in the light (microwaves) of the CMB that inflation would be expected to produce.   (Many more details:   web resources from the BICEP team and partner institutions;  quick semi-technical gloss on the results from Sean B. Carroll;  Matt Strassler’s take; Dennis Overbye’s account in the NYT.)

One key caveat before the wind up:  this is one result from one group.  It is reported with great confidence (that five sigma claim).  But something this big needs independent confirmation — data from the Planck satellite for example, or more ground based observations from other microwave detectors.  This isn’t yet a done deal.

Such confirmation (or disproof) will come fairly quickly — a few years at most.

In the meantime, assuming the data do hold up, what would that mean (forgive me) more cosmically?

At the very least:  that we now understand in previously unattainable detail how our current habitat emerged from nothing (or better, “nothing”).  That the idea of a multiverse — other patches of space time that underwent an inflationary episode to form island universes of their own — has now gained a boost (if one patch of space-time can inflate, so could others)….

…or to put in mythic terms:  there is grandeur in this view of life (the cosmos).  Paraphrasing an old friend, astronomer Sandra Faber, with this new, richer, more fully realized picture of the birth of the universe we have once again enriched that creation story that only science tells, the one that connects the earth we inhabit today with a process of cosmic evolution that we now can trace back all the way to just the barest instant this side of the point of origin.

A good day.

*To a close approximation — this is physics.  You want certainty, become a mathematician.

[Thanks to Dr Katherine J. Mack of the University of Melbourne, aka @AstroKatie, who helped make sure no egregious errors slipped through.  Any mistakes, major or minor, that remain are mine, all mine.]

Image:  J. W. M. Turner, The Beacon Lightc. 1840

PS:  Bonus video showing one of the founding architects of inflation theory receiving news of the result:

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2 Comments on “The Most Exciting Sentence I’ve Read This Decade…”

  1. […] there was this big story in cosmology the other day– Tom Levenson’s write-up is very nice– which has been hailed as one of the greatest discoveries since the last greatest discovery, […]

  2. […] We get a nice, clear history of the theory-building in the decades before BICEP2, plus a brief summary of the findings and some implications, from Tom Levenson, who blogs at The Inverse Square. One of those implications is “That the idea of a multiverse — other patches of space time that underwent an inflationary episode to form island universes of their own — has now gained a boost (if one patch of space-time can inflate, so could others)….” […]

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